Chronic soft-tissue (or myofascial) pain is a significant public health problem. Despite its high prevalence, the underlying mechanisms are poorly understood. In particular, very little is known about the pathophysiology and soft tissue environment of a myofascial trigger point (MTrP). MTrPs are palpable, localized painful nodules in a taut band of skeletal muscle that are a characteristic finding in myofascial pain syndrome (MPS). MTrPs are associated with spontaneous referred pain in symptomatic patients, and are the target for current management strategies for MPS, such as dry needle therapy. Recently, our research group has developed new ultrasound imaging methods to visualize and characterize the physiology and physical properties of the MTrPs and their surrounding soft tissue; and microanalytic techniques to assay the local biochemical milieu. These innovative methodological advances provide a unique opportunity to integrate the physical, physiological and biochemical findings to achieve a more comprehensive understanding of the abnormalities associated with MTrPs (e.g., muscle, fascia, blood vessels); and to correlate these findings with clinical assessments to better understand the role of MTrPs in chronic pain. Our ultimate goal is to develop a working model of the underlying mechanisms of MTrPs and translate the findings to objective clinical outcome measures using office-based technology. The specific aims of the project are: 1) To determine the mechanical tissue properties, vascular physiology and biochemical milieu of the affected soft tissue neighborhood of active MTrPs in patients with chronic neck pain compared to asymptomatic control subjects with/without palpable MTrPs; and 2) To determine the effect of a physical perturbation caused by dry needle therapy, a widely accepted method of treatment, on the soft tissue environment and biochemical milieu of active MTrPs in symptomatic subjects. Our working hypothesis is that MTrPs are sites of muscle injury where local biochemical changes lead to sustained muscle contracture, compression of blood vessels and a local energy crisis that causes tissue hypoxia. This condition perpetuates the release of inflammatory cytokines and nociceptive (pain-inducing) substances. To test this hypothesis, we will correlate ultrasound imaging scores, analyte levels and functional clinical measures in our specific aims. To translate these findings into clinical outcome measures that can be used in an office-based setting, we will adapt a reliable and inexpensive 3D Tactile Imaging instrument for quantifying mechanical soft tissue changes associated with MTrPs.